Line upgrade
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This document discusses transforming an existing 220 kV double circuit transmission line into a 400 kV single circuit line using twin conductors. It analyzes the technical feasibility and provides the procedures, including system study, analysis of tower strength, possible configurations, clearance requirements, and cost benefits compared to building a new transmission line. Upgrading the existing line requires less land acquisition and has lower costs than new construction while meeting the increasing electricity demand.
![ Possible configurations are indicated towards the preliminary
study conducted over the data available for existing towers [1].
POSSIBLE CONFIGURATIONS
6](https://image.slidesharecdn.com/lineupgrade-170211095521/85/Line-upgrade-6-320.jpg)
![UPRATING
Line modification that yields increase in current flow
limits is known as uprating [2].
Conductors are normally operated below the thermal
rating of the line.
Current flow is increased to operate the conductor
closer to its thermal limit.
Reconductoring the line with HTLS conductor is one
of the solutions.
9](https://image.slidesharecdn.com/lineupgrade-170211095521/85/Line-upgrade-9-320.jpg)
![PRINCIPLE OF AN
INSULATOR
Freedom of movement provided
to the conductor determines the
clearance required for the line
[3].
Clearance should be provided
for both inward and outward
swing of the conductor.
For a suspension insulator,
freedom of movement is very
high and hence more clearance
will be required.
16](https://image.slidesharecdn.com/lineupgrade-170211095521/85/Line-upgrade-16-320.jpg)
![INSULATED CROSSARM
Insulated crossarms are polymer
insulators that directly fixed to the
tower [4].
This eliminates the use of metallic
crossarm.
With the freedom of movement
restricted, the conductors swing
will be reduced significantly.
This reduces the required live -
metal clearance level and thus
making the line compact.
17](https://image.slidesharecdn.com/lineupgrade-170211095521/85/Line-upgrade-17-320.jpg)
![CALCULATION FOR CONDUCTOR
SURFACE GRADIENT:
The conductor surface gradient is calculated from the following
equation [5]:
E = (V/√3)*(b/(r*ln ((a/Re)*2h/ √(4h2+a2))))
where
E : conductor surface voltage gradient (kV/cm)
V : line voltage (kV)
b : factor for multiple conductors
r : radius of conductor (cm)
R : outside radius of bundle (cm)
Re : equivalent radius of bundle conductor (cm)
S : distance between component conductor centers (cm)
a : phase spacing (cm)
h : height of conductor above ground (cm)
n : number of component conductors in bundle
23](https://image.slidesharecdn.com/lineupgrade-170211095521/85/Line-upgrade-23-320.jpg)
Line upgrade
- 1. TRANSFORMING EXISTING 220 kV D/C LINE INTO 400 kV S/C LINE (TWIN CONDUCTORS) CASE STUDY TOWARDS THE ENQUIRY FLOATED BY RELIANCE INFRASTRUCTURE SUPREME & CO. PVT. LTD. P-200, BENARAS ROAD, HOWRAH -711108, WEST BENGAL, INDIA Phone : +91-033-26516701 TO 05 Fax : +91-033-26516706 Email : sales@supreme.in & info@supreme.in Website : www.supreme.in 1
- 2. WHY UPRATING / UPGRADING IS REQUIRED ? Existing and planned infrastructures have made it extremely difficult to build new transmission line to meet the electricity demand-supply gap. It becomes highly pertinent to uprate or upgrade the already existing line rather than constructing new transmission line.2
- 3. PROCEDURE System study Analysis Design and validation Implementation 3
- 4. SYSTEM STUDY Study on existing power transmission system for selecting the optimum solution. Conceptual study for optimal solution regarding the upgrading of the existing 220 kV double circuit transmission line corridor. 4
- 5. ANALYSIS OF SYSTEM Identify an optimum alternative to upgrade the transmission line corridor. Evaluate the performance of the power transmission system. Investigating the capability of existing towers and foundations to withstand new mechanical loadings. Undertake financial analysis for most promising alternative. Estimate cost of various alternatives.5
- 6. Possible configurations are indicated towards the preliminary study conducted over the data available for existing towers [1]. POSSIBLE CONFIGURATIONS 6
- 7. Technical advantages No new land acquisition cost Cost of erection is minimized Minimize environmental restriction Reduces cost of maintenance Visually aesthetics Foot print remains the same* * If the foundation has to be strengthened, there may be a mere increase in fo7
- 8. INCREASING POWER RATING Power in a circuit is increased by: Uprating (increase in current flow). Upgrading (increase in voltage level). Both upgrading and uprating. Surge impedance loading. 8
- 9. UPRATING Line modification that yields increase in current flow limits is known as uprating [2]. Conductors are normally operated below the thermal rating of the line. Current flow is increased to operate the conductor closer to its thermal limit. Reconductoring the line with HTLS conductor is one of the solutions. 9
- 10. HIGH PERFORMANCE CONDUCTOR Carbon fibre core High operating temperature Ampacity twice as that of ACSR. Low sag. Higher Aluminium content. Resistance comparatively low. 10
- 11. HIGH PERFORMANCE CONDUCTOR FITTINGS Supreme has developed and conducted electrical tests on conductor fittings, specifically designed for HTLS conductors. Since HTLS conductors operate at higher temperature, they require special type of clamps and fittings. 11
- 12. LINE UPGRADING Modifications that allow operation at higher voltage level. Results in higher increase in power flow, compared to uprating. Percentage voltage drop decreases. Need to replace substation equipments. Maintaining the electrical clearance increase as per the voltage rating by reconfiguring insulator and12
- 13. FACTORS TO BE CONSIDERED FOR LINE UPGRADING Electrical Clearance. RoW acquisition (may be required in exceptional cases). Civil and structural modifications (may be required). Mitigation of Corona and Radio Interference Voltage (RIV). 13
- 14. CLEARANCES FOR 400 kV AC Nominal Voltage 400 kV Minimum clearance above ground 8.84 m Minimum live metal clearance 2.6 m Minimum phase to phase clearance 3.9 m Angle of shield (maximum) 200 Minimum mid span clearance 9 m 14
- 15. METHODS ADOPTED FOR UPGRADING Insulated Crossarms Inter Phase Spacers Intermediate Structures Change of Conductor and Earthwire 15
- 16. PRINCIPLE OF AN INSULATOR Freedom of movement provided to the conductor determines the clearance required for the line [3]. Clearance should be provided for both inward and outward swing of the conductor. For a suspension insulator, freedom of movement is very high and hence more clearance will be required. 16
- 17. INSULATED CROSSARM Insulated crossarms are polymer insulators that directly fixed to the tower [4]. This eliminates the use of metallic crossarm. With the freedom of movement restricted, the conductors swing will be reduced significantly. This reduces the required live - metal clearance level and thus making the line compact. 17
- 18. INTER PHASE SPACERS Inter Phase Spacers are used to maintain phase to phase clearance even under high wind condition. This reduces short circuit problems encountered in many high voltage lines. Composite insulators which has high strength to weight ratio are mainly used as inter phase spacer.18
- 19. INTERMEDIATE STRUCTURE If an intermediate structure is needed after final analysis, we could opt the use of monopoles. Monopoles will require lesser foot print when compared with a lattice tower. Foot print can be restricted as per the availability of space 19
- 20. DISCONNECTION OF EXISTING LINK DURING UPGRADING Line shutdown is required for making the erection works. Temporary towers, supported by guy wires without civil foundations, can be installed in parallel with existing line. Line will be disconnected only at the time of by-passing. Power outage will only be in the20
- 21. Conductor type ACSR Code name Moose Diameter 31.77 mm Area 597 sq mm Weight 2.004 kg/m UTS 16438 kgf CONDUCTOR DETAILS 21
- 22. CORONA INCEPTION VALUE The voltage gradient necessary to produce corona at the conductor surface is given by, 𝐸0 = 30 ∗ 𝑚 1 + 0.301 𝑟 where r : radius of the conductor and m : surface irregularity factor For example, consider Moose conductor with radius 1.5885 cm and surface irregularity factor, m= 0.80 We get, E0 = 30.76 kV/cm. Beyond or near this value, the conductor has corona effect. 22
- 23. CALCULATION FOR CONDUCTOR SURFACE GRADIENT: The conductor surface gradient is calculated from the following equation [5]: E = (V/√3)*(b/(r*ln ((a/Re)*2h/ √(4h2+a2)))) where E : conductor surface voltage gradient (kV/cm) V : line voltage (kV) b : factor for multiple conductors r : radius of conductor (cm) R : outside radius of bundle (cm) Re : equivalent radius of bundle conductor (cm) S : distance between component conductor centers (cm) a : phase spacing (cm) h : height of conductor above ground (cm) n : number of component conductors in bundle 23
- 24. FOR SINGLE CONDUCTOR FOR TWIN CONDUCTOR Number of Conductors in Bundle: 1 Number of Conductors in Bundle: 2 Rated Voltage: 400 kV Rated Voltage: 400 kV Phase Spacing: 390 cm Phase Spacing: 390 cm Height of Conductor above Ground: 884 cm Height of Conductor above Ground: 884 cm Voltage Gradient E = 26.5316 kV/cm Voltage Gradient E = 20.4383 kV/cm Distance between Component Conductors: Conductors: 45 cm R =22.5000 cm Re = 8.0246 cm β = 0.5318 RESULTS OF CORONA CALCULATION 24
- 25. SAG-TENSION CALCULATION SPAN: 335 m; WIND ZONE: 3; TERRAIN CATEGORY: 1 LOADING CONDITION SAG (m) TENSION (kgf) Initial Condition 7.664 2983.640 48° C Full Wind 5.805 3939.268 48° C 28% Wind 8.192 2791.232 48° C No Wind 8.613 2654.896 85° C Full Wind 6.585 3472.508 85° C 28% Wind 9.517 2402.742 85° C No Wind 10.039 2277.604 25
- 26. RESULTS FROM TECHNICAL AND FINANCIAL EVALUATION Costs are substantially reduced when compared with the costs of a new 400 kV OHL. No land or right of way acquisition is necessary for project implementation compared with the new line solution. Minimum environmental impact. 26
- 27. REFERENCES 1. D. Marginean, E. Mateescu, H.S. Wechsler, G. Florea, C. Matea, “Transforming Existing 220 kV Double Circuit Line into 400 kV Single Circuit Line in Romania”, IEEE- 2011. 2. Manual on Transmission Line, CBIP, 2014. 3. EPRI Transmission Line Reference Book—115-345 kV Compact Line Design, “The Blue Book”, 2008. 4. K. Papailiou, F. Schmuck, “Silicone Composite Insulators: Materials, Design, Applications”, Springer, 2012. 5. Cigre Green Book on Overhead Lines, 2014. 27
- 28. THANK YOU SUPREME & CO. PVT. LTD. P-200, BENARAS ROAD, HOWRAH -711108, WEST BENGAL, INDIA Phone : +91-033-26516701 TO 05 Fax : +91-033-26516706 Email : sales@supreme.in & info@supreme.in Website : www.supreme.in 28